l\ elation between Nucleolus and Chromosomes. 57 



also, as Child holds in the case of Arcnicola marina, several fibers may 

 have united into one. Some of the astral rays interdigitate above the equa- 

 torial plate. All seem to merge into the cytoreticulum. Frequent cross- 

 connections are seen. The central ends of the rays are seen to penetrate 

 for some distance into the centrosphere, but they could never be traced 

 as far as the central granules (centrosome). It is very probable that 

 the rays are centrally continuous with the reticulum (very delicate, and 

 sometimes alveolar in structure) of the centrosphere. The spindle now 

 begins to rotate and ultimately assumes a radial position. This rotation is 

 effected very rapidly. In 10 to 15 minutes more the first polar body is fully 

 formed. Thus it requires about I hour for the first polar body to form, 

 which agrees with what was observed in the case of living eggs. To 

 recapitulate, the single aster appears about 10 minutes after transference 

 of the eggs to sea-water. At twenty minutes there are two asters some 

 distance apart, with rays extending through the ruptured nuclear wall and 

 becoming attached to the growing chromosomes. At 45 minutes the first 

 polar spindle is fully formed and in process of rotation. The last 20 or 

 30 minutes represent the prophase of maturation. The spindle moves rap- 

 idly into a radial position, metaphase and anaphase are passed through very 

 quickly, and after 60 minutes the first polar body is fully formed. 



In the radial position, the spindle is at first comparatively slender and 

 sharply pointed at the ends (figs. 66, 67). The central sphere often contains 

 two centrosomes (fig. 66). The spindle moves bodily toward the periphery 

 and as it approaches the cell-wall it becomes stouter, somewhat barrel-shaped, 

 slightly shorter, and its ends less pointed (fig. 69). This change of shape 

 and size is undoubtedly due to the resistance met with by the spindle in 

 its passage through the cytoplasm. The outwardly pointing rays of the 

 distal pole disappear, the horizontal rays are at first bent inward, and all 

 eventually disappear into the cytoreticulum as the outer pole of the spindle 

 is forced out of the egg to form the first polar body (fig. 70). The rays 

 of the central aster have also meanwhile become shorter and less definite, 

 while the centrosphere has become more reticular, somewhat flattened, very 

 much less definite, and in the later stages of the first polar spindle is scarcely 

 to be recognized. In the late anaphase the spindle exhibits a distinct mid- 

 body (Zwischenkorper) in the form of swellings or small granules in the 

 equatorial plane of the spindle. This marks the line of division between 

 the first polar body and the central pole of the spindle. Traces of spindle 

 fibers are at first visible in the first polar body, but these gradually disappear, 

 and the chromosomes (about 18 double dumb-bell-shaped bodies, often 

 assuming the form of " tetrads ") are seen to lie in a homogeneous or finely 

 granular light-staining substance (figs. 70, 71). In my study of the living 

 eggs I found a single instance of a division of the first polar body. Study of 

 sectioned material failed to contribute a duplicate of this solitary example. 



